[davidmanze]

That Sigma is an APS-C lens design (so a fast standard zoom), this Tamron is a 135 format "full frame" design (so a fast UWA zoom on FF). This new Tamron is more a competitor to the Sony A-mount 16-35mm f2.8, Sony FE 16-35mm f4, Canon EF 16-35mm f2.8 L IS USM II, Canon EF 16-35mm f4 L IS USM, Nikkor AF-S 16-35mm f4 VR, Nikkor AF-S 14-24mm f2.8, Sigma 12-24mm, Tokina 17-35mm f4, Tokina 16-28mm f2.8 and the upcoming Canon EF 11-24mm f4 L USM. 

 

The front element is indeed excluding "normal" filters (just like with the Nikkor 14-24mm, Sigma 12-24mm, upcoming Canon 11-24mm, Tokina 16-28mm).

Yes, your right! I forgot about the FF aspect, however I see it finding it's way onto a lot of APSc bodies just because of it's 2.8 aperture.

 

We'll have to see how it performs!